Methods and devices for constructively using the pressure pulsations in reciprocating compressors installations

ABSTRACT

Apparatuses and methods for constructively utilizing pressure pulses to enhance the volumetric efficiency of a reciprocating compressor are provided. An apparatus includes a gas circulation device and a controller. The gas circulation device provides a path through which the gas circulates between a reciprocating compressor and a volume bottle buffering the reciprocating compressor from an installation. The gas circulation device is configured to have a resonance frequency substantially equal to a frequency of the performing compression cycles in the reciprocating compressor. The controller is configured to control timing of switching a valve located between the reciprocating compressor and the gas circulation device in order to constructively use pressure pulsations occurring in the gas circulation device, to enhance the volumetric efficiency of the reciprocating compressor.

BACKGROUND OF THE INVENTION

Embodiments of the subject matter disclosed herein generally relate toinstallations using reciprocating compressors in the oil and gasindustry, and, more particularly, to constructively using the pressurepulsations to enhance the volumetric efficiency of the compressor, thatis, achieving a pulse charging effect.

Compressors used in the oil and gas industry have to meet industryspecific requirements that take into consideration, for example, thatthe compressed gas is frequently corrosive and flammable. The AmericanPetroleum Institute (API), the organization that sets the recognizedindustry standard for equipment used in the oil and gas industry, hasissued a document, API618, listing a complete set of minimumrequirements for reciprocating compressors.

The compressors may be classified in positive displacement compressors(for example, reciprocating, screw, or vane compressors) and dynamiccompressors (for example, centrifugal or axial compressors). In thepositive displacement compressors, the compression is achieved bytrapping the gas and then reducing volume in which the gas is trapped.In the dynamic compressors, the compression is achieved by transformingthe kinetic energy (for example, of a rotating element) into pressureenergy at a predetermined location inside the compressor.

An ideal compression cycle (graphically illustrated in FIG. 1 bytracking evolution of pressure versus volume) includes at least fourphases: expansion, suction, compression and discharge. When thecompressed fluid is evacuated from a compression chamber at the end of acompression cycle, a small amount of fluid at the delivery pressure P₁remains trapped in a clearance volume V₁ (that is, the minimum volume ofthe compression chamber). During the expansion phase 1 and the suctionphase 2 of the compression cycle, the piston moves to increase thevolume of the compression chamber. At the beginning of the expansionphase 1, the delivery valve closes (the suction valve remaining closed),and then, the pressure of the trapped fluid drops since the volume ofthe compression chamber available to the fluid increases. The suctionphase of the compression cycle begins when the pressure inside thecompression chamber becomes equal to the suction pressure P₂, triggeringthe suction valve to open at volume V₂. During the suction phase 2, thecompression chamber volume and the amount of fluid to be compressed (atthe pressure P₂) increase until a maximum volume of the compressionchamber V₃ is reached.

During the compression and discharge phases of the compression cycle,the piston moves in a direction opposite to the direction of motionduring the expansion and suction phases, to decrease the volume of thecompression chamber. During the compression phase 3 both the suction andthe delivery valves are closed (that is, the fluid does not enter orexit the cylinder), the pressure of the fluid in the compression chamberincreasing (from the suction pressure P₂ to the delivery pressure P₁)because the volume of the compression chamber decreases to V₄. Thedelivery phase 4 of the compression cycle begins when the pressureinside the compression chamber becomes equal to the delivery pressureP₁, triggering the delivery valve to open. During the delivery phase 4the fluid at the delivery pressure P₂ is evacuated from the compressionchamber until the minimum (clearance) volume V₁ of the compressionchamber is reached.

One measure of the efficiency of the compressor is the volumetricefficiency, which is a ratio of the volume of the compression chamberswept by the piston of the reciprocating compressor during the suctionphase V₃−V₂ to the total volume V₃−V₁ swept by the piston during thecompression cycle.

The phenomenon of pressure pulsations occurring outside thereciprocating compressor is due to the discontinued nature of the gasflow inside the reciprocating compressor. These pressure pulsations maylead to large vibrations and fatigue stresses, high noise level, andreduced compressor performance. API618 includes the detailedrequirements for an acoustical study that has to be undertaken whendesigning an installation including a reciprocating compressor, for,among other purposes, avoiding the damaging effect of the pressurepulsations. In order to prevent these pulsations from propagatingthroughout the installation, volume bottles are installed before thesuction valves and after the discharge valves of the compressors,buffering the reciprocating compressor from the rest of theinstallation.

For example, FIG. 2 illustrates a simplified model of an interfacebetween a reciprocating compressor 10 and the rest of the installation.Here the term “interface” designates all the components between a valve20 of the reciprocating compressor 10 and a plant pipe 30 through whichgas is channeled to or from a rest of the installation (for example, anoil and gas plant). The reciprocating compressor 10 has a piston 40, andis connected via a pipe 50 to a volume bottle 60. The volume bottle 60is then connected to the oil and gas plant via the plant pipe 30.

The volume bottle 60 filled with the gas to be compressed or thecompressed gas (depending on whether the volume bottle is located beforethe suction valve or after the discharge valve or the reciprocatingcompressor 10) has a high acoustical impedance and operates as areflector of the pulsations, allowing only a small fraction to betransmitted towards the plant pipe 30.

The frequency of the pressure pulsations generated by the reciprocatingcompressor 10 is the frequency of the compression process in thereciprocating compressor. Resonance occurs when a natural frequency f ofthe pipe 30 equals the frequency of the pressure pulsations generated bythe reciprocating compressor. The natural frequency f of the pipe 50depends on the speed of sound in the gas c and the length L of the pipe50. In a first approximation, the following relationship exists betweenthese quantities: f=c/(2L). If stationary pressure waves are formedalong the pipe 50, orifices (that is, localized narrowings of the pipe)may be employed to reduce the amplitude of the stationary pressurewaves.

Thus, conventionally, the pressure pulsations (that inherently occur dueto discontinued nature of the gas flow in a reciprocating compressor)are dissipated, not used.

It would be desirable to provide methods and devices (included orperformed in oil and gas installations including a reciprocatingcompressor) that use constructively the pressure pulsation to enhancethe efficiency of the reciprocating compressor.

BRIEF DESCRIPTION OF THE INVENTION

Some of the embodiments have an actuated valve and a gas circulationdevice configured to have a resonance frequency substantially equal to afrequency of performing compression cycles in the reciprocatingcompressor. The valve is actuated such as to enhance the volumetricefficiency of the compressor using constructively the inherent pressurepulsations. This manner of using the pressure pulses to enhanceefficiency is known as the pulse charging effect.

According to an exemplary embodiment, an apparatus is provided. Theapparatus includes a gas circulation device and a controller. The gascirculation device provides a path through which gas to be compressedcirculates between a reciprocating compressor and a volume bottlebuffering the reciprocating compressor from an installation. The gascirculation device is configured to have a resonance frequencysubstantially equal to a frequency of the performing compression cyclesin the reciprocating compressor. The controller is configured to controltiming of switching a valve located between the reciprocating compressorand the gas circulation device in order to constructively use thepressure pulsations occurring in the gas circulation device, to enhancea volumetric efficiency of the reciprocating compressor.

According to another exemplary embodiment, a method of using a pulsecharging effect to enhance a volumetric efficiency of a reciprocatingcompressor is provided. The method includes providing a gas circulationdevice between a valve of the reciprocating compressor and a volumebottle buffering the reciprocating compressor from an installation. Thegas circulation device is configured to have a resonance frequency thatis substantially equal to a frequency of performing compression cyclesin the reciprocating compressor. The method further includes controllingtiming of actuating the valve to constructively use the pressure pulsesinherently occurring in the gas circulation device, to enhance thevolumetric efficiency of the reciprocating compressor.

According to another exemplary embodiment, a method for retrofitting areciprocating compressor installation is provided. A reciprocatingcompressor of the installation has an output or an input thereofbuffered by a volume bottle from the rest of the installation. Thereciprocating compressor installation is retrofitted to use a pulsecharging effect of the reciprocating compressor to enhance a volumetricefficiency thereof. The method includes modifying a gas circulationdevice by connecting an output or an input of the reciprocatingcompressor to the volume bottle. This is accomplished by adding at leastone acoustic resonator to a pipe of the gas circulation device, to makethe gas circulation device to have a resonance frequency substantiallyequal to a frequency of performing compression cycles in thereciprocating compressor. The method further includes connecting a valvebetween the reciprocating compressor and the gas circulation device, toa controller configured to control timing of actuating the valve inorder to use constructively pressure pulsations occurring in the gascirculation device, to enhance a volumetric efficiency of thereciprocating compressor.

These and other aspects and advantages of the present invention willbecome apparent from the following detailed description considered inconjunction with the accompanying drawings. It is to be understood,however, that the drawings are designed solely for purposes ofillustration and not as a definition of the limits of the invention, forwhich reference should be made to the appended claims. Moreover, thedrawings are not necessarily drawn to scale and, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. In thedrawings:

FIG. 1 is a pressure versus volume graph illustrating an idealcompression cycle;

FIG. 2 is a schematic diagram of a conventional interface between areciprocating compressor and an oil and gas plant;

FIG. 3 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 4 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 5 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 6 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 7 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 8 is a schematic diagram of an interface between a reciprocatingcompressor and an oil and gas plant, according to an exemplaryembodiment;

FIG. 9 is flow chart of a method of using pulsations inherentlygenerated during operation of a reciprocating compressor in order toenhance compressor's efficiency, according to an exemplary embodiment;and

FIG. 10 is a flow chart of a method for retrofitting a reciprocatingcompressor installation, according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

The following description of the exemplary embodiments refers to theaccompanying drawings. The same reference numbers in different drawingsidentify the same or similar elements. The following detaileddescription does not limit the invention. Instead, the scope of theinvention is defined by the appended claims. The following embodimentsare discussed, for simplicity, with regard to the terminology andstructure of reciprocating compressors used in an oil and gas plant(that is, installation or equipment). However, the embodiments to bediscussed next are not limited to this system, but may be applied toother similar technical conditions.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the subject matter disclosed. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout the specification is not necessarily referringto the same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

In some embodiments described below, a gas circulation device, whichprovides a path through which gas (to be compressed or after beingcompressed) circulates between a reciprocating compressor (that is, thecompression chamber thereof) and a volume bottle. The gas circulationdevice is configured to have a resonance frequency substantially equalto a frequency of performing compression cycles in the reciprocatingcompressor. Furthermore, a valve located between the compression chamberand the gas circulating device is controlled to open relative to a phaseof the pressure pulsations near the valve in the gas circulation devicesuch that to enhance efficiency of the compressor.

If one considers that the valve is the suction valve, an increasedpressure in the gas circulation device near the suction valve while thevalve is open results in a larger amount of gas entering the volume ofthe compression chamber to be compressed. The suction taking place at ahigher pressure P₂+Δp, where Δp is due to the pulse charging effect, isillustrated as a dashed line in FIG. 1. Since the volume V₂′corresponding to the intersection of the dashed line with the linerepresenting the expansion phase 1 is smaller than V₂, the volumetricefficiency increases because the numerator of the ratio defining thevolumetric efficiency increases V₃−V₂′>V₃−V₂.

In fact, Δp is not a constant offset of the pressure as it varies intime, between a maximum positive value and a maximum negative value. Acontroller may determine the opening moment of the valve 20 to have amaximum pressure Δp (added or subtracted) at the time of opening of thevalve or achieve an overall pressure higher than the suction pressureduring (or at the end of) the suction phase.

FIG. 3 is a schematic diagram of an interface 100 (such as, anapparatus) between a reciprocating compressor 10 and a volume bottle 60providing a gas volume buffer to an oil and gas plant according to anexemplary embodiment. The large volume of gas in the volume bottle 60prevents or substantially dampens pressure pulses occurring in gasoutside the reciprocating compressor 10 due to flux variation in thereciprocating compressor 10 (such as, due to the pulse charging effect).The interface 100 includes a gas circulation device and a controller110. The gas circulation device provides a path through which the gas(to be compressed or after being compressed) circulates between thereciprocating compressor 10 and the volume bottle 60. The gascirculation device is configured to have a resonance frequencysubstantially equal to a frequency of performing compression cycles inthe reciprocating compressor. The gas circulation device includes a pipe130 and an in-line resonator 140 having an area larger than the pipearea. The exact location of the in-line resonator 140 along the pipe 130does not affect the acoustic characteristics of the gas circulationdevice.

The controller 110 controls an actuator (not shown) actuating the valve120. That is, the controller 110 controls timing of actuating the valve120 relative to the phase of the pressure pulses (due to the pulsecharging effect) near the valve such that to use the pressure pulses toenhance the volumetric efficiency of the compressor. If the valve 120 isthe suction valve, the controller 110 controls the timing of actuatingthe valve 120 to have a maximum pressure value Δp added to the suctionpressure, while the valve 120 is open (that is, during the suction phaseof the compressing cycle).

In another exemplary embodiment illustrated in FIG. 4, the gascirculation device of an interface 101 includes a side branch resonator150 in addition to the in-line resonator 140. Optionally, theside-branch resonator 150 may be connected to the in-line resonator 140via a resonator valve 160. The resonator valve 160 may be switched toconnect or to disconnect the side-branch resonator 150 to/from the pipe130, depending on the composition of the gas (whose composition affectsthe speed of sound in the gas and therefore the resonance frequency ofthe gas circulation device). The controller 110 may control theresonator valve 160.

In another exemplary embodiment illustrated in FIG. 5, the gascirculation device of an interface 102 includes a side-branch pipe 170instead of the in-line resonator 140. Optionally, the side-branch pipe170 may be connected to the pipe 130 via a resonator valve 180. Theresonator valve 180 may be switched to connect or to disconnect theside-branch pipe 170 to/from the pipe 130, for example, depending on thecomposition of the gas (whose composition affects the speed of sound inthe gas and therefore the resonance frequency of the gas circulationdevice). The controller 110 may control the resonator valve 180.

Alternatively, in another exemplary embodiment illustrated in FIG. 6,the gas circulation device of an interface 103 includes a side-branchresonator 200 attached to the pipe 130. Optionally, the side-branchresonator 200 may be connected to the pipe 130 via a resonator valve210. The resonator valve 210 may be switched to connect or to disconnectthe side-branch resonator 200 to/from the pipe 130, for example,depending on the composition of the gas (whose composition affects thespeed of sound in the gas, and, therefore, the resonance frequency ofthe gas circulation device). The controller 110 may control theresonator valve 210.

In another embodiment illustrated in FIG. 7, a gas circulation device ofan interface 104 includes an additional side-branch resonator 220connected to the side-branch resonator 200. Optionally, the side-branchresonator 200 and/or the additional side-branch resonator 220 may beconnected to pipe 130 and to the side-branch resonator 200,respectively, via resonator valves 210 and 230, respectively. Theresonator valves 210 and 230 may be switched to connect or to disconnectthe side-branch resonator 200 and the additional side-branch resonator220, respectively, depending on the composition of the gas (whoseaffects the speed of sound in the gas, and, therefore, the resonancefrequency of the gas circulation device). The controller 110 may controlthe resonator valve 210 and/or 230.

In another embodiment illustrated in FIG. 8, the gas circulation deviceof the interface 105 has the side-branch resonator 200 connected to thevolume bottle via a secondary pipe 240. A resonator valve 250 located onthe secondary pipe 240 is switched depending on the composition of thegas.

In various embodiments illustrated in FIGS. 3-8 and other equivalentembodiments, it is executed a method 300 of using pulsations inherentlygenerated outside, but due to operating the reciprocating compressor, toenhance the volumetric efficiency of the compressor. As illustrated inFIG. 9, the method 300 includes providing a gas circulation devicebetween a valve of the reciprocating compressor and a volume bottlebuffering the reciprocating compressor from an oil and gas plant, thegas circulation device being configured to have a resonance frequencysubstantially equal to a frequency of performing compression cycles inthe reciprocating compressor, at S310. The method 300 further includescontrolling the timing of actuating the valve to use pressure pulsesinherently occurring in the gas circulation device due to the pulsecharging effect, to enhance the volumetric efficiency of thereciprocating compressor, at S320.

In an embodiment, the providing S310 of method 300 may include adding aside-branch resonator or a side-branch pipe to a pipe connecting thevalve to the volume bottle. In another embodiment, the providing S310 ofmethod 300 may include switching one or more resonator valves connectingacoustic resonators to a pipe connecting the valve to the volume bottle.

An existing reciprocating compressor installation may be retrofitted tobecome able to use pulsations inherently generated during operation ofthe reciprocating compressor to enhance the compressor's efficiency.FIG. 10 is a flow chart of a method 400 for retrofitting thereciprocating compressor installation, according to an exemplaryembodiment. The method 400 includes modifying a gas circulation deviceby connecting an output or an input of the reciprocating compressor tothe volume bottle, by adding at least one acoustic resonator to a pipeof the gas circulation device, to make the gas circulation device tohave a resonance frequency substantially equal to a frequency ofperforming compression cycles in the reciprocating compressor, at S410.The method 400 further includes connecting a valve between thereciprocating compressor and the gas circulation device, to a controllerconfigured to control timing of actuating the valve in order to usepressure pulsations occurring in the gas circulation device due to apulse charging effect of the reciprocating compressor, to enhance avolumetric efficiency of the reciprocating compressor, at S420.

In an embodiment of the method 400, the at least one acoustic resonatormay include an in-line acoustic resonator, a side-branch acousticresonator or a side-branch pipe. In another embodiment, the method 400may further include connecting the at least one acoustic resonator tothe apparatus via a resonator valve.

The disclosed exemplary embodiments provide apparatuses (devices) andmethods for using constructively the pressure pulses (that is, the pulsecharging effect) occurring around the reciprocating compressors due tothe flow variation, to enhance the volumetric efficiency of thecompressor. It should be understood that this description is notintended to limit the invention. On the contrary, the exemplaryembodiments are intended to cover alternatives, modifications andequivalents, which are included in the spirit and scope of the inventionas defined by the appended claims. Further, in the detailed descriptionof the exemplary embodiments, numerous specific details are set forth inorder to provide a comprehensive understanding of the claimed invention.However, one skilled in the art would understand that variousembodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodimentsare described in the embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the embodiments or in various combinations with or withoutother features and elements disclosed herein.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims.

Thus, while there has been shown and described and pointed outfundamental novel features of the invention as applied to exemplaryembodiments thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit of the invention. Moreover, it isexpressly intended that all combinations of those elements and/or methodsteps which perform substantially the same function in substantially thesame way to achieve the same results are within the scope of theinvention. Furthermore, it should be recognized that structures and/orelements and/or method steps shown and/or described in connection withany disclosed form or embodiment of the invention may be incorporated inany other disclosed or described or suggested form or embodiment as ageneral matter of design choice. It is the intention, therefore, to belimited only as indicated by the scope of the claims appended hereto.

What is claimed is:
 1. An apparatus, comprising: a gas circulationdevice that provides a path through which a gas to be compressedcirculates between a reciprocating compressor and a volume bottlebuffering the reciprocating compressor from an installation, the gascirculation device being configured to have a resonance frequencysubstantially equal to a frequency of the performing compression cyclesin the reciprocating compressor; and a controller configured to controltiming of switching a valve located between the reciprocating compressorand the gas circulation device in order to constructively use thepressure pulsations occurring in the gas circulation device to enhance avolumetric efficiency of the reciprocating compressor.
 2. The apparatusof claim 1, wherein the gas circulation device comprises: a pipe and anin-line resonator having an area larger than the pipe area, wherein thepipe and the in-line resonator are located in-between the reciprocatingcompressor and the volume bottle.
 3. The apparatus of claim 2, whereinthe gas circulation device further comprises a side-branch resonator,located laterally to the in-line resonator, wherein the side-branchresonator is connected to the in-line resonator through a resonatorvalve, the resonator valve being switched between being opened and beingclosed thereby connecting or disconnecting the side-branch resonator tothe in-line resonator depending on a composition of the gas.
 4. Theapparatus of claim 1, wherein the gas circulation device comprises: apipe located between the reciprocating compressor and the volume bottle;and a side-branch pipe located laterally to the pipe, wherein theside-branch pipe is connected to the pipe through a resonator valve, theresonator valve being switched between being opened and being closedthereby connecting or disconnecting the side-branch pipe to the pipedepending on a composition of the gas.
 5. The apparatus of claim 4,wherein the gas circulation device further comprises an additionalside-branch resonator connected to the side resonator.
 6. The apparatusof claim 5, wherein at least one of the side-branch resonator and theadditional side-branch resonator is connected through a valve to thepipe or to the side-branch resonator, respectively, the valve beingswitched between being opened and being closed thereby connecting ordisconnecting the side-branch pipe or the additional side-branchresonator thereof depending on a composition of the gas.
 7. Theapparatus of claim 1, wherein the gas circulation device comprises: apipe located between the reciprocating compressor and the volume bottle;and a side-branch pipe located laterally to the pipe, wherein theside-branch pipe is connected to the pipe through a resonator valve, theresonator valve being switched between being opened and being closedthereby connecting or disconnecting the side-branch pipe to the pipedepending on a composition of the gas.
 8. The apparatus of claim 1,wherein the valve is a suction valve, and wherein the controllercontrols the timing of actuating the valve to have a maximum pulsationpressure added to a suction pressure while the valve is open.
 9. Amethod of using a pulse charging effect to enhance a volumetricefficiency of a reciprocating compressor, the method comprising:providing a gas circulation device between a valve of the reciprocatingcompressor and a volume bottle buffering the reciprocating compressorfrom an installation, wherein the gas circulation device is configuredto have a resonance frequency that is substantially equal to a frequencyof performing compression cycles in the reciprocating compressor; andcontrolling timing of actuating the valve to constructively use thepressure pulses inherently occurring in the gas circulation device toenhance the volumetric efficiency of the reciprocating compressor.
 10. Amethod for retrofitting a reciprocating compressor installation in whichan output or an input of a reciprocating compressor is buffered by avolume bottle from the rest of the installation, the installation beingretrofitted to use a pulse charging effect of the reciprocatingcompressor to enhance a volumetric efficiency thereof, the methodcomprising: modifying a gas circulation device by connecting an outputor an input of the reciprocating compressor to the volume bottle, byadding at least one acoustic resonator to a pipe of the gas circulationdevice, to make the gas circulation device to have a resonance frequencysubstantially equal to a frequency of performing compression cycles inthe reciprocating compressor; and connecting a valve between thereciprocating compressor and the gas circulation device to a controllerconfigured to control timing of actuating the valve in order toconstructively use the pressure pulsations occurring in the gascirculation device, to enhance a volumetric efficiency of thereciprocating compressor.